A BIG One!
Last June I gave my sister's husband a tuber of our new introduction, Wyn's Conquistador. He had never grown a dahlia before in his life but loves our giants & decided he wanted to try & grow a big one. I think he succeeded!! By the time the pict. was taken it was a bit past it's prime & starting to go to center, but you get the idea. It was 17" wide & 13" deep.
So, you see, you don't have to be an expert- even novices can grow dahlias- big or small!